Increasingly, the effort to keep “bath salts” and synthetic marijuana off the shelves of stores and away from thrill-seeking drug-users is turning into a madcap chase — a game of fox-and-hound between law enforcement and people tweaking the chemical make-up of the drugs.

In New Jersey last week, state Attorney General Jeff Chiesa announced a 270-day emergency order to criminalize sales and possession of synthetic marijuana, and gave purveyors 10 days to get rid of it. Last year New Jersey banned bath salts, the synthetic drugs that mimic cocaine, methamphetamine or LSD.

“This action is necessary because of the unique nature of synthetic marijuana and other designer drugs,” Chiesa said. “When one product was banned, the dealers and manufacturers found it all too easy to evade the law by creating new toxic products that have similar effects on the brain but were not specifically identified as illegal.”

Pennsylvania outlawed both types of drugs last year, but a series of busts in February showed that sales of bath salts and synthetic pot continue — and some of the substances may fall outside prosecution because they aren’t identical to the formulas banned by legislation.

That’s no surprise. Most of these drugs are coming from overseas, and it’s relatively easy to substitute a chemical or subtly alter its makeup to sidestep the law.

So what’s the answer? Federal action, right?

Last week the Drug Enforcement Administration extended a federal ban on five chemicals used to make the synthetic drugs, for six months. Yet federal legislation calling for a comprehensive ban has been blocked by Sen. Rand Paul, R-Ky., who says anti-drug efforts should be left to the states. Paul also has allies who believe a federal prohibition will just extend a failed “war on drugs” and perpetuate, rather than solve, the problem.

There’s something to be said for that last point. Sending users and low-level drug dealers to prison is little more than taxpayer welfare for a corrections system addicted to its own growth. Adding synthetic drugs to this mentality makes as much sense as categorizing marijuana with heroin.

But what’s not arguable is that these designer drugs are dangerous. They can produce elevated blood pressure, hallucinations and seizures, violence and the occasional death. They are attractive to young people as an alternative to drugs that may be harder to obtain.

And they’re legal. Or they’re illegal and being sold with the knowledge that authorities might not be able to make charges stick.

Education, awareness and parental oversight are the keys to prevention — but we know these tactics can’t totally block the allure of drug escape to both young people and adults.

Chiesa, the New Jersey attorney general, is correct — this is an emergency. It’s not going to be solved by a patchwork of state laws and county-by-county crackdowns. There’s a need to address the alchemy that could generate an endless supply of synthetic drugs, and that must come from the top. From Congress.

As for demand … if we can’t get the point across to young people about the dangers of bath salts and synthetic pot, then a market will always be there. But we have to do more to get them off, and keep them off, store shelves.